Grease, rolling bearing, constant velocity joint, and rolling parts

ABSTRACT

The present invention provides grease which prevents frictional wear on a lubricating surface and excellent in performance of preventing occurrence of flaking, heat-resistant performance, and long-term durability, a grease-enclosed rolling bearing, a constant velocity joint, and rolling parts. Grease is composed of base grease, essentially containing a thickener, to which at least 0.01 to 15 wt % of one substance selected from among bismuth and inorganic bismuth compounds is added. The inorganic bismuth compounds are at least one inorganic bismuth selected from among bismuth sulfate, bismuth trioxide, bismuth carbonate, and sodium bismuthate. The above-described grease is used for the rolling bearing and the constant velocity joint. A coating film of at least one substance selected from among the bismuth and the inorganic bismuth is formed on surfaces of the rolling parts.

TECHNICAL FIELD

The present invention relates to grease excellent in lubricatingproperties under a high load and high in withstand load; a rollingbearing and a constant velocity joint in which the grease is enclosed;and rolling parts for use in airplanes, rolling stocks, buildingmachines, auxiliary machines of cars, and hubs of cars.

The rolling bearing relates to the rolling bearing for use in a wheel ora wheel-supporting rolling bearing unit. The rolling bearing for use inthe wheel relates to a bearing for use in an axle of the rolling stock,a rolling bearing for use in the rolling stock to be used for a mainmotor of the rolling stock, a rolling bearing for use in thewheel-supporting apparatus for rotatably supporting wheels of a car whena car is suspended by a suspending apparatus, and a rolling bearing foruse in a rolling neck of a rolling machine.

The constant velocity joint relates to a constant velocity joint of aplunging type for use in a car or a constant velocity ball joint of afixed type for use in a car and a constant velocity joint in which theabove-described grease is enclosed.

BACKGROUND ART

Heretofore, when the rolling bearing in which grease is enclosed is usedin a high load-applied condition, a lubricating film of lubricatinggrease is liable to fracture. When the lubricating film fractures, metalcontact occurs to generate a disadvantage that heat generation andfrictional wear increase. Therefore by using grease containing anextreme-pressure agent (EP agent), the disadvantage is decreased.

As the use condition of the rolling bearing becomes severe, by improvingthe lubricating properties of grease and the resistance thereof to aload, it is necessary to prevent the occurrence of the metal contactcaused by the fracture of the lubricating oil film. A roller bearing hasa flange and at a flange portion thereof, a rolling element and a flangeof a bearing ring make a sliding motion. Thus at the flange portion, thefracture of the lubricating oil film is liable to occur.

Solid lubricant-containing grease in which for 100 parts by weight of anadduct of melamine (iso) cyanurate, 5 to 1000 parts by weight of a solidlubricant selected from the group of polytetrafluoroethylene, molybdenumdisulfide, and molybdenum dithiocarbamate (thereinafter abbreviated asMoDTC) is used is known (patent document 1). An organic bismuthcompound-containing an extreme-pressure grease lubricant composition foruse in the rolling bearing is also known (patent document 2). Greasecontaining the MoDTC and polysulfide to decrease wear is also known(patent document 3).

The bearing for use in the rolling stock is classified into the bearingfor use in the axle and the bearing for use in the main motor. In thecase of the bearing for use in the axle, both end portions of the axleis supported by a tapered roller bearing mounted on an underframe of therolling stock. In the case of the bearing for use in the main motor,both output-side end portions of the rotary shaft of the motor aresupported by a cylindrical roller bearing or a ball bearing mounted onthe underframe of the rolling stock.

In a wheel-supporting apparatus supporting a non-driven wheel such as afront wheel of a rear wheel-driving type vehicle, two rolling bearingsare mounted on an axle (knuckle spindle) provided on a steering knuckle,a flange is provided on an outside-diameter surface of an axle hubrotatably supported by the rolling bearings, and a braking drum of abraking apparatus and a wheel disk of the wheel are mounted, with studbolts provided on the flange and with nuts engaging the stud bolts withscrews.

A back plate is mounted on the flange provided on the steering knuckleso that the back plate supports a braking mechanism for imparting abraking force to the braking drum.

In the above-described wheel-supporting apparatus, as the rollingbearing rotatably supporting the axle hub, a tapered roller bearinghaving a high load capacity and a high rigidity is used. The taperedroller bearing is lubricated with grease enclosed between the axle andthe axle hub.

As an example of the bearing for use in the rolling stock and thewheel-supporting apparatus to which a high load is applied at ahigh-speed operation, a bearing for use in the rolling stock in whichgrease containing not more than 20 wt % of an organic metal compoundcontaining metal selected from among nickel, tellurium, selenium,copper, and iron for the entire amount of the grease is enclosed isknown (patent document 4).

In a rolling neck bearing for use in a rolling machine, generally, aninner ring thereof has one double row inner ring, and an outer ring hasone double row outer ring and two single row outer rings disposed atboth ends of the double row outer ring via a spacer. Rolling elementsare circumferentially rotatably disposed in four rows between the innerring and the outer ring. An annular seal member is mounted on both endportions of the outer ring.

The rolling neck bearing for use in the rolling machine is used in arolling process of a steel-manufacturing factory in an environment inwhich a rolling liquid containing water as its main component is jetted.Thus there is a problem that when water penetrates into the bearing, alubricating oil film is fractured and the bearing is damaged at an earlystage owing to inferior lubrication.

To cope with this problem, an example of the rolling neck bearing havingthe following construction is known: An annular seal member is mountedat both end portions of the outer ring, with a seal lip portion thereofin contact with the peripheral surface of the inner ring. Anintermediate seal member is mounted at an inner peripheral side of abutted end of one double row inner ring. By forming a slit for a ventmechanism on the intermediate seal member, even though air inside thebearing expands or contracts owing a change of temperature, thedifference between a pressure inside the bearing and a pressure outsidethe bearing is automatically balanced to prevent the water frompenetrating into the bearing (patent document 5).

However, the rolling bearing having the above-described construction isused as the rolling neck bearing for use in the rolling machine, theseal lip portion of the annular seal member mounted on the outer ring atboth axial ends thereof is of a type which makes a line contact with theperipheral surface of the inner ring. Thus in an environment in whichthe rolling roller is frequently mounted and removed for re-grinding,the seal lip portion is much damaged. Consequently rolling water andcooling water penetrate into the bearing at a rate of not more than 20%of the grease and mix with a lubricant (normally, grease lubricant inwhich lithium-based thickener such as Adlex, Albania or the like isused), thus deteriorating the lubricating function thereof and causingthe bearing to be damaged in an early stage owing to inferiorlubrication.

Regarding the rolling bearing unit for supporting the wheel of a car, arolling bearing of a first example having the construction in which theinner ring is set as the stationary-side bearing ring and the hub is setas the rotational-side bearing ring is known. A rolling bearing of asecond example having the construction in which the outer ring is set asthe stationary-side bearing ring and the hub is set as therotational-side bearing ring is known (patent document 6).

The first example of the conventional construction of thewheel-supporting rolling bearing unit is described below with referenceto FIG. 12. FIG. 12 is a sectional view showing the first example of theconventional construction of the wheel-supporting rolling bearing unit.The wheel 1 is rotatably supported by the wheel-supporting rollingbearing unit 2 as shown in FIG. 12 at the end portion of the shaft 3constructing the suspending construction. That is, the inner rings 5, 5,set as the stationary-side bearing ring, which construct thewheel-supporting rolling bearing unit 2 are fitted on the axle 4 fixedto the end portion of the shaft 3 and fixed thereto with the nut 6. Thewheel 1 is fixedly connected to the hub 7, set as the rotational-sidebearing ring, which constructs the wheel-supporting rolling bearing unit2 with a plurality of the studs 8, 8 and the nuts 9, 9.

The double row outer ring rolling surfaces 10 a, 10 b each serving asthe rotational-side rolling surface are formed on the inner peripheralsurface of the hub 7, and the mounting flange 11 is formed on theperipheral surface thereof. The wheel 1 and the drum 12 for constructingthe braking apparatus are fixedly connected to one side surface (outerside surface in the illustrated example) of the mounting flange 11 withthe studs 8, 8 and the nuts 9, 9.

In the specification, “outside” in the axial direction means the outerside in the widthwise direction in a state in which the bearing unit ismounted on a vehicle, whereas “inside” means the central side in thewidthwise direction.

Between the outer ring rolling surfaces 10 a, 10 b and between the innerring rolling surfaces 13 a, 13 b formed on the peripheral surfaces ofthe inner rings 5, 5 as the stationary-side rolling surfaces, aplurality of the balls 14, 14 which are the rolling elementsrespectively are rotatably provided, with the balls 14, 19 held by thecages 15, 15 respectively. By combining the constituent members with oneanother in this manner, a double row ball bearing of an angular type isconstructed in a back-to-back arrangement, and the hub 7 is rotatablysupported on the periphery of each of the inner rings 5, 5, and a radialload and a thrust load are freely supported. The seal rings 16 a, 16 bare provided between the inner peripheral surfaces of both end portionsof the hub 7 and the peripheral surface of the end portion of each ofthe inner rings 5, 5 to disconnect the space in which the balls 14, 19are provided and the inner space 17 from each other.

The open portion at the outer end of the hub 7 is closed with the cap18.

When the above-described wheel-supporting rolling bearing unit 2 isused, as shown in FIG. 12, the axle 4 on which the inner rings 5, 5 arefixedly fitted is fixed to the shaft 3, and the wheel 1 and the drum 12with which an unshown tire is combined are fixed to the mounting flange11 of the hub 7. The drum 12, and an unshown wheel cylinder and anunshown shoe both supported by the backing plate 19 fixed to the endportion of the shaft 3 are combined with one another to construct thedrum brake for braking use. At a braking time, a pair of shoes providedat an inside-diameter side of the drum 12 is pressed against the innerperipheral surface of the drum 12. Grease is enclosed inside the innerspace 17 to lubricate the rolling contact portion among the outer ringrolling surfaces 10 a, 10 b, the inner ring rolling surfaces 13 a, 13 b,and the rolling surfaces of the balls 14, 14.

The second example of the conventional construction of thewheel-supporting rolling bearing unit is described below with referenceto FIG. 13. FIG. 13 is a sectional view showing the second example ofthe conventional construction of, the wheel-supporting rolling bearingunit. In the case of the wheel-supporting rolling bearing unit 2 a shownin FIG. 13, the hub 7 a serving as the rotational-side bearing ring isrotatably supported by a plurality of the balls 14, 14 each serving asthe rolling element at the inside-diameter side of the outer ring 20serving as the stationary-side bearing ring. To do so, the double rowouter ring rolling surfaces 10 a, 10 b each serving as thestationary-side rolling surface are formed on the inner peripheralsurface of the outer ring 20, and the first and second inner ringrolling surfaces 21, 22 each serving as the rotational-side rollingsurface are formed on the peripheral surface of the hub 7 a. The hub 7 ais constructed in combination of the hub body 23 and the inner ring 24.The mounting flange 11 a for supporting the wheel is provided at theouter end of the peripheral surface of the hub body 23. The first innerring rolling surface 21 is formed at the intermediate portion of the hubbody 23. The small-diameter stepped portion 25 whose diameter is smallerthan that of the portion where the first inner ring rolling surface 21is formed is provided at the portion near the inner end of theintermediate portion of the hub body 23. The inner ring 24 having thesectionally circular arc-shaped second inner ring rolling surface 22formed on the peripheral surface thereof is fitted on the small-diameterstepped portion 25. Further the inner end surface of the inner ring 24is held down by the caulking portion 26 formed by plastically deformingthe inner end portion of the hub body 23 radially outward to fix theinner ring 24 to the hub body 23.

Seal rings 16 c, 16 d are provided between the inner peripheral surfacesof both end portions of the outer ring 20 and the peripheral surface ofthe intermediate portion of the hub body 23 as well as the peripheralsurface of the inner end portion of the inner ring 24 to disconnect theinner space 17 a in which the balls 14, 14 are provided and the outerspace from each other between the inner peripheral surface of the outerring 20 and the peripheral surface of the hub 7 a.

Grease is enclosed in the inner space 17 a to lubricate the rollingcontact portion among the outer ring rolling surfaces 10 a, 10 b, theinner ring rolling surfaces 21, 22, and the rolling surfaces of theballs 14, 14.

In the lubrication of the rolling bearing portion, to prevent thelubricating film of the lubricating grease from being fractured, thegrease containing the extreme-pressure agent (EP agent) is used toreduce the fracture of the lubricating oil film.

For example, the extreme-pressure grease lubricant compositioncontaining the organic bismuth compound for use in the rolling bearingis known (patent document 2). The grease containing the MoDTC andpolysulfide to reduce wear is also known (patent document 3).

It cannot be said that the constant velocity joint is satisfactory in asevere operation condition generated in recent high-performance cars.Any of the constant velocity joint of a double off-set type, theconstant velocity joint of a cross groove type, and the like used as theconstant velocity joint of the plunging type and a bar field joint usedas the constant velocity ball joint of a stationary type has aconstruction of transmitting a torque by means of several balls. Inthese constant velocity joints, owing to a reciprocating motion ofcomplicated rolling and sliding under a high surface pressure duringrotations thereof, a stress is repeatedly applied to balls and metalsurfaces that contact the balls. Thus a flaking phenomenon is liable tooccur owing to metal fatigue. Because a car is lightweight in recentyears so that an engine is capable of producing a high output and fuelexpenses can be decreased, the constant velocity joint is small-sized.Thus the constant velocity joint is subjected to a relatively highsurface pressure. Consequently the conventional grease is incapable ofsufficiently preventing the occurrence of the flaking phenomenon.Further it is necessary to improve the heat resistance of the grease.

Heretofore to prevent the fracture of the lubricating film of thelubricating grease, the extreme-pressure agent (EP agent)-containinggrease is used for the above-described grease for use in the constantvelocity joint to decrease the fracture of the lubricating oil film ofthe lubricating grease.

For example, the grease (patent document 7) obtained by mixing anorganic molybdenum compound with urea-based grease and the grease(patent document 8) obtained by mixing molybdenum disulfide, the MoDTC,and a sulfur-containing organic tin compound with the urea-based greaseare known.

Because the rolling bearing and the constant velocity joint are used ina severe condition of a high speed and under a high load, the flange ofthe bearing ring makes a sliding motion on the large, end face of theroller and the flange portion thereof. Thus the lubricating oil film ofthe lubricating grease is liable to fracture. Owing to the fracture ofthe lubricating oil film, metal contact occurs to generate adisadvantage that heat generation and frictional wear increase.

Therefore by improving the lubricating properties of the grease and thewithstand load at a high speed and under a high load, it is necessary toprevent the occurrence of the metal contact caused by the fracture ofthe lubricating oil film. Thus by using the extreme-pressureagent-containing grease, its disadvantage is decreased.

The rolling bearing and the constant velocity joint are subjected torolling friction between the rolling surface of the inner ring as wellas the rolling surface of the outer ring and a “roller” which is arolling element and subjected to sliding friction between the flangeportion and the “roller”. Because the sliding friction is larger thanthe rolling friction, seizing of the flange portion is liable to occurwhen the use condition becomes severe. Therefore the conventionalrolling bearing and the conventional constant velocity joint have aproblem respectively that they cause a grease-exchanging work to befrequently performed and are incapable of making maintenance free.

Further as the use condition of the rolling bearing and that theconstant velocity joint become severe, for example, when they arelubricated at a high speed of not less than 100,000 in dN value, theconventional grease is incapable of preventing the occurrence of theflaking phenomenon sufficiently. Thus it is difficult to use theconstant velocity joint.

In the case of the conventional rolling parts and the rolling bearing,when the grease-enclosed rolling bearing is used under a high load, thelubricating oil film of the lubricating grease is liable to fracture.When the lubricating oil film has fractured, metal contact occurs togenerate a disadvantage that heat generation and frictional wearincrease. Thus the grease containing the extreme-pressure agent (EPagent) is used to reduce the disadvantage of the lubricating oil film.

To provide a sliding member or a rolling member and a rolling bearinghaving a low friction, a low wear, and sufficiently improved withstandload and seizing, base grease is allowed to chemically react with atleast one of an organic phosphor compound, an organic sulfur compound,an organic chlorine compound, and an organic metal compound. Thereby thesliding member or the rolling member having a film layer formed by thereaction of compounds in a thickness of 0.05 to 0.5 μm as a result ofthe chemical reaction is obtained (patent document 9).

To improve the frictional characteristics of rolling parts in a boundarylubrication condition so that the rolling parts have little variationsin the frictional characteristics thereof and have a stable and longlife in the bearings thereof, a rolling part on which a coating film ofmetal salts of thiophosfate is formed is known (patent document 10).

But these rolling parts have a problem that they are insufficient inwear-decreasing effect on sliding surfaces thereof and lack long-termdurability in the use condition of a high temperature and a high speed.

In the grease-enclosed rolling bearing, as the use condition of therolling bearing becomes severe, it is necessary to prevent theoccurrence of the metal contact caused by the fracture of thelubricating oil film by improving the lubricating properties of greaseand the resistance thereof to a load. The roller bearing has inparticular the flange, and at the flange portion, the rolling elementand the flange of the bearing ring make a sliding motion respectively.Thus the grease-enclosed rolling bearing has a problem that at theflange portion, the fracture of the lubricating oil film is liable tooccur.

-   Patent document 1: Japanese Patent Application Laid-Open No.    61-12791-   Patent document 2: Japanese Patent Application Laid-Open No. 8-41478-   Patent document 3: Japanese Patent Application Laid-Open No.    10-324885-   Patent document 4: Japanese Patent Application Laid-Open No.    10-17884-   Patent document 5: Japanese Patent Application Laid-Open No.    2000-104747-   Patent document 6: Japanese Patent Application Laid-Open No.    2001-221243-   Patent document 7: Japanese Patent Application Laid-Open No.    63-46299-   Patent document 8: Japanese Patent Application Laid-Open No.    10-183161-   Patent document 9: Japanese Patent Application Laid-Open No.    2-256920-   Patent document 10: Japanese Patent Application Laid-Open No.    11-30236

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The problem to be solved by the invention is to provide grease whichprevents frictional wear on a lubricating surface in a state in which arolling sliding motion is generated at a high speed and under a highload and is excellent in the performance of preventing the occurrence offlaking and in heat-resistant performance and long-term durability, agrease-enclosed rolling bearing, a grease-enclosed constant velocityjoint, and rolling parts.

Means for Solving the Problems

A grease of the present invention is composed of a base grease and anadditive, wherein the base grease comprises a base oil and a thickener,and the additive comprises a substance selected from among bismuth andinorganic bismuth compounds (“inorganic bismuth compound” is hereinafterreferred to as “inorganic bismuth”).

0.01 to 15 wt % of at least one substance selected from the bismuth andthe inorganic bismuth is added to a total amount of the base grease andthe additive.

The bismuth is bismuth powder.

The inorganic bismuth is one inorganic bismuth selected from amongbismuth sulfate, bismuth trioxide, bismuth carbonate, and sodiumbismuthate.

The base oil is at least one oil selected from among poly-α-olefin oil,mineral oil, ester oil, and ether oil.

The base oil has a kinematic viscosity of 20 to 200 mm²/s at 40° C.

The thickener is at least one compound selected from among urea-basedcompounds and lithium soap.

A rolling bearing of the present invention has an inner ring, an outerring, a plurality of rolling elements interposed between the inner ringand the outer ring, and the above-described grease is applied to aperiphery of the rolling elements.

In a constant velocity joint of the present invention, a rotationaltorque is transmitted by engagement between a track groove and a rollingelement, and by rolling of the rolling element along the track groove,an axial movement thereof is performed, and the above-described greaseis enclosed in the constant velocity joint.

A rolling part of the present invention has a coating film of onesubstance selected from among bismuth and inorganic bismuth formed on asurface thereof and is used in contact with the above-described grease.

Effect of the Invention

At least one substance selected from among the bismuth and the inorganicbismuth excellent in the resistance to heat and durability thereof isused for the grease, grease-enclosed rolling bearing, constant velocityjoint, and rolling parts of the present invention. Therefore thesubstance supplied to a sliding interface forms a coating film, thusallowing the extreme-pressure property effect to continue for a longtime. Therefore in the state in which rolling and sliding motions aregenerated at a high speed and under a high load, frictional wear on thelubricating surface is prevented, and the grease, grease-enclosedrolling bearing, constant velocity joint, and rolling parts of thepresent invention can be preferably utilized for rolling stocks,building machines, electric auxiliary machines of cars, and the likedemanded to prevent the occurrence of flaking, have heat-resistantperformance and long-term durability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partly cut-out perspective view of a roller bearing.

FIG. 2 is a partly cut-out perspective view of a tapered roller bearing.

FIG. 3 is a sectional view of a deep groove ball bearing.

FIG. 4 shows an extreme-pressure property evaluation test apparatus.

FIG. 5 is a sectional view of a bearing for use in an axle.

FIG. 6 is a sectional view of a wheel-supporting apparatus.

FIG. 7 is a sectional view of a bearing for use in a rolling neck of arolling machine.

FIG. 8 is a sectional view of a first example of the construction of awheel-supporting rolling bearing unit.

FIG. 9 is a sectional view of a second example of the construction ofthe wheel-supporting rolling bearing unit.

FIG. 10 is a sectional view of a third example of the construction ofthe wheel-supporting rolling bearing unit.

FIG. 11 is a sectional view of a fourth example of the construction ofthe wheel-supporting rolling bearing unit.

FIG. 12 is a sectional view of a first example of the conventionalconstruction of the wheel-supporting rolling bearing unit.

FIG. 13 is a sectional view of a second example of the conventionalconstruction of the wheel-supporting rolling bearing unit.

FIG. 14 shows results of an extreme-pressure property evaluation test.

FIG. 15 shows results of durability test of a rolling bearing.

FIG. 16 is a partly cut-out sectional view of a constant velocity jointof a double off-set type.

FIG. 17 is a partly cut-out sectional view of a constant velocity jointof a tri-port type.

FIG. 18 is an illustration of an entire wind power generator including amain shaft-supporting apparatus for wind power generation.

FIG. 19 shows the main shaft-supporting apparatus for wind powergeneration.

FIG. 20 shows a mounting construction of a main shaft-supporting bearingof the main shaft-supporting apparatus for wind power generation.

EXPLANATION OF REFERENCE NUMERALS AND SYMBOLS

-   1: wheel-   2: wheel-supporting rolling bearing unit-   3: shaft-   4: axle-   5: inner ring-   6: nut-   7: hub-   8: stud-   9: nut-   10: outer ring rolling surface-   11: mounting flange-   12: drum-   13: inner ring rolling surface-   14: ball-   15: cage-   16: seal ring-   17: inner space-   18: cap-   19: backing plate-   20: outer ring-   21: inner ring rolling surface-   22: inner ring rolling surface-   23: hub body-   24: inner ring-   25: small-diameter stepped portion-   26: caulking portion-   27: external thread portion-   28: nut-   29: spline hole-   31: grease-enclosed bearing-   32: inner ring-   33: outer ring-   34: rolling element-   35: cage-   36: seal member-   37: grease-   38: open portion at both axial ends-   41: rotary shaft-   42: ring-shaped specimen-   43: ring-shaped specimen-   44: end surface-   51: tapered roller bearing-   52: inner ring-   53: outer ring-   54: tapered roller-   55: axle-   56: inner ring spacer-   57: injection hole-   61: tapered roller bearing-   62: steering knuckle-   63: flange-   64: axle-   65: axle hub-   66: flange-   67: stud bolt-   68: nut-   69: braking drum-   70: wheel disk-   71: rim-   72: back plate-   73: grease cap-   81: tapered roller bearing-   82: inner ring-   83: inner ring rolling surface-   84: outer ring-   85: outer ring rolling surface-   86: tapered roller-   87: cage-   88: seal member-   89: large flange-   90: seal case-   91: annular groove-   92: contact-type oil seal-   101: inner ring-   102: outer ring-   103: track groove-   104: track groove-   105: ball-   106: cage-   107: spherical surface-   108: spherical surface-   109: shaft-   110: boot-   111: grease for use in constant velocity joint-   112: outer ring-   113: track groove-   114: tri-port member-   115: leg-like shaft-   116: spherical roller-   117: needle-   121: wind power generator-   122: blade-   123: main shaft-   124: nacelle-   125: bearing-   126: speed-up gear-   127: generator-   128: supporting base-   129: motor-   130: reduction gear-   131: inner ring-   132: outer ring-   133: rolling element-   134: cage-   135: bearing housing-   136: seal-   140: swing bearing

BEST MODE FOR CARRYING OUT THE INVENTION

As a result of investigation of improvement of the lubricating propertyand withstand load of a bearing in a state in which rolling and slidingmotions are generated at a high speed and under a high load, it has beenfound that a rolling bearing, a constant velocity joint, and rollingparts composed of grease containing 0.01 to 15 wt % of bismuth orinorganic bismuth used for the entire grease as an additive are worn toa lower extent and have a higher long-term durability under a high loadand in a sliding motion than a rolling bearing, a constant velocityjoint, and rolling parts composed of grease containing an additive otherthan the bismuth or the inorganic bismuth. It has been also found thatrolling bearings using the above-described bearing for use in wheelssuch as a rolling bearing for use in a rolling stock, a rolling bearingfor use in a wheel-supporting apparatus, a rolling bearing for use in arolling neck of a rolling machine, and a wheel-supporting rollingbearing unit using the above-described bearing are worn to a lowerextent and have a higher long-term durability under a high load and in asliding motion.

This is because a coating film consisting of the bismuth, the inorganicbismuth or the like is superior to other substances in the heatresistance and durability thereof and is less heat-decomposable than theother substances. Thus it is considered that they are capable of keepingan extreme-pressure property effect for a long time. The presentinvention is based on the above-described finding.

It is essential to add the bismuth or the inorganic bismuth to thegrease of the present invention as an extreme-pressure agent. One kindof the bismuth or the inorganic bismuth may be added to the grease ortwo kinds thereof may be mixed with each other to add a mixture to thegrease. The addition amount of the bismuth or the inorganic bismuth isset to 0.01 to 15 wt % for the entire grease and preferably 1 to 10 wt%. When the addition amount thereof is less than 0.01 wt %, the effectof improving the wear resistance cannot be displayed. When the additionamount thereof is more than 15 wt %, a torque at the time of a rotationbecomes large, and thus heat generation increases and the rotation isinterfered.

As the bismuth or the inorganic bismuth that can be used for the greaseof the present invention, bismuth (powder), bismuth carbonate, bismuthchloride, bismuth nitrate, and hydrates thereof, bismuth sulfate,bismuth fluoride, bismuth bromide, bismuth iodide, bismuth oxyfluoride,bismuth oxychloride, bismuth oxybromide, bismuth oxyiodide, bismuthoxide, and hydrates thereof, bismuth hydroxide, bismuth selenide,bismuth telluride, bismuth phosphate, bismuth oxyperchlorate, bismuthoxysulfate, sodium bismuthate, bismuth titanate, bismuth zirconate, andbismuth molybdate are listed. In the present invention, the bismuthpowder, the bismuth sulfate, and bismuth trioxide are favorable becausethese substances are excellent in resistance to heat and durability andless heat-decomposable than other substances and thus have a highextreme-pressure property effect. The bismuth powder and the bismuthtrioxide or mixtures thereof are particularly favorable.

The bismuth is a silver white metal, has the lowest heat conductivity ofall metals except mercury, has a specific gravity of 9.8, and a meltingpoint of 271.3° C. The bismuth powder is a comparatively soft metal andbecomes easily filmy when it is subjected to an extreme pressure.Therefore the diameter of the bismuth powder should be so set that it iscapable of dispersing in the grease. It is preferable that the bismuthpowder for use in the grease of the present invention to be enclosed inthe bearing for use in the rolling stock has a diameter of 5 to 500 μm.

It is essential to add the bismuth or the inorganic bismuth to thegrease for use in the rolling bearing, the constant velocity joint, andthe rolling parts of the present invention as the extreme-pressure agentthereof. One kind of the bismuth or the inorganic bismuth may be addedto the grease or two kinds thereof may be mixed with each other to add amixture to the grease.

The addition amount of the bismuth or the inorganic bismuth is set to0.01 to 15 wt % for the entire grease and preferably 1 to 10 wt %. Whenthe addition amount thereof is less than 0.01 wt %, the effect ofimproving the wear resistance cannot be displayed. When the additionamount thereof is more than 15 wt %, the torque at the time of arotation becomes large, and thus heat generation increases, and therotation is interfered.

As the base oil that can be used for the grease of the presentinvention, mineral oil, PAO oil, ester oil, phenyl ether oil, fluorineoil, and hydrocarbon oil (GTL base oil) synthesized by Fischer-Tropschreaction are listed. Of these oils, it is preferable to use at least onebase oil selected from among the PAO oil and the mineral oil. Normallythe above-described PAO oil is oligomers of α-olefin or isomerizedα-olefin or mixtures of polymers. As examples of the α-olefin, it ispossible to list 1-octane, 1-nonen, 1-decene, 1-dodecene, 1-tridecene,1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene,1-nonadecene, 1-eicosene, 1-docosene, 1-tetracosene, and the like.Normally mixtures of these substances are used. As the mineral oil, itis possible to use any of normal lubricants such as paraffin mineraloil, naphthene mineral oil, and the like and those used in the field ofgrease.

It is preferable that the base oil which can be used for the grease tobe enclosed in the rolling bearing of the present invention has akinematic viscosity of 20 to 200 mm²/s at 40° C. It is not preferablethat the base oil has a kinematic viscosity less than 20 mm²/s becausethe evaporation loss thereof increases and resistance thereof to heatdeteriorates. It is not preferable that the kinematic viscosity of thebase oil exceeds 200 mm²/s because the temperature of the bearing risesgreatly owing to an increase of the rotational torque.

It is preferable that the base oil which can be used for the grease tobe enclosed in the rolling bearing of the present invention for use in awheel and a wheel-supporting rolling bearing unit has a kinematicviscosity of 30 to 200 mm²/s at 40° C. It is not preferable that thebase oil has a kinematic viscosity less than 30 mm²/s because theevaporation loss thereof increases and resistance thereof to heatdeteriorates. It is not preferable that the kinematic viscosity of thebase oil exceeds 200 mm²/s because the temperature of the bearing risesgreatly owing to the increase of the rotational torque.

It is preferable that the base oil which can be used for the grease tobe enclosed in the constant velocity joint of the present invention hasa kinematic viscosity of 30 to 500 mm²/s at 40° C. It is not preferablethat the base oil has a kinematic viscosity less than 30 mm²/s becausethe evaporation loss thereof increases and resistance thereof to heatdeteriorates. It is not preferable that the kinematic viscosity of thebase oil exceeds 500 mm²/s because the temperature of the bearing risesgreatly owing to the increase of the rotational torque.

As a thickener that can be used for the grease of the present invention,it is possible to use aluminum, lithium, sodium, metallic soap-basedthickeners such as composite lithium, composite calcium, and compositealuminum; and diurea compounds shown by a formula (1) shown below. Thediurea compounds are favorable. These thickeners may be used singly orin combination of two or more thereof.

R₂ in the formula (I) indicates an aromatic hydrocarbon radical havingcarbon atoms of 6 to 15. R₁ and R₃ indicate an aromatic hydrocarbongroup having carbon atoms of 6 to 12, an alicyclic hydrocarbon grouphaving carbon atoms of 6 to 20 or an aliphatic hydrocarbon group havingcarbon atoms of 6 to 20. R₁ and R₃ may be identical to or different fromeach other.

The urea-based compound indicated by the formula (I) is obtained by areaction of diisocyanate and monoamine. As the diisocyanate, phenylenediisocyanate, diphenyl diisocyanate, diphenylmethane diisocyanate,1,5-naphthylene diisocyanate, 2,4-trilene diisocyanate,3,3-dimethyl-4,4-biphenylene diisocyanate, octadecane diisocyanate,decane diisocyanate, hexane diisocyanate, and the like are listed. Asthe monoamine, octyl amine, dodecyl amine, hexadecyl amine, stearylamine, oleyl amine, aniline, p-toluidine, cyclohexyl amine, and the likeare listed.

The urea compound is obtained by a reaction between an isocyanatecompound and an amine compound. To prevent a reactive free radical fromremaining, it is preferable to use the isocyanate group of theisocyanate compound and the amino group of the amine compound in anequivalent weight.

By mixing the urea compound with the base oil, base grease to whichvarious compounding agents are to be added is obtained. The base greaseis formed by reacting the isocyanate compound and the amine compoundwith each other in the base oil.

In addition to the urea compound, polyurea compounds can be used.

It is preferable that the mixing consistency of the grease, which can beused in the present invention, for use in the rolling bearing and theconstant velocity joint is in the range from 160 to 400. When the mixingconsistency is less than 160, the lubricating performance at a lowtemperature is low. When the mixing consistency exceeds 400, the greaseis liable to leak. Thus it is not preferable that the mixing consistencyis less than 160 and more than 400.

In the present invention, it is possible to use the rolling bearing towhich lubricating oil or a lubricant such as lubricating grease isapplied or in which the lubricating oil or the lubricant is enclosed.The above-described lubricant is not limited to a specific kind, butlubricants that are normally used for the rolling bearing can be used.The rolling bearing of the present invention can be used even in a statein which no lubricant is used therefor.

Known additives can be contained in the grease of the present invention.As the additives, it is possible to list organic zinc compounds;antioxidants such as amine-based antioxidant, phenol-based antioxidant,sulfur-based antioxidant; metal inert agents such as benzotriazole,sodium nitride, and the like; viscosity index-improving agents such aspolymethacrylate, polystyrene, and the like; and solid lubricants suchas molybdenum disulfide, graphite, and the like. These additives can beadded to the grease singly or in combination of two or more thereof.

In the grease of the present invention for use in the constant velocityjoint, as the mixing ratio of the additive, it is preferable that 0.01to 15 parts by weight is used for 100 parts by weight which is the totalamount of the base oil and the thickener. When the mixing ratio of theadditive is less than 0.01 parts by weight, the effect of the mixingthereof is small. When the mixing ratio of the additive agent is morethan 15 parts by weight, heat generation increases. Thus temperaturerises.

As the mixing ratio of the base oil, it is preferable that 50 to 95parts by weight of the base oil is used for 100 parts by weight which isthe total amount of the base oil and the thickener. When the mixingratio of the base oil is less than 50 parts by weight, the amount of thelubricating oil is small and hence inferior lubrication is liable tooccur. When the mixing ratio of the base oil exceeds 95 parts by weight,the grease is liable to become soft and hence liable to leak.

The grease of the present invention that can be used for the rollingbearing for use in a wheel, the constant velocity joint, and the rollingparts can be also used for bearings, to which a high load is applied,other than the rolling bearing for use in a wheel, the constant velocityjoint, and the rolling parts.

The grease of the present invention for use in the roller bearing iscapable of improving the life of the grease-enclosed roller bearing.Therefore the grease of the present invention for use in the rollerbearing can be used as grease to be enclosed in a cylindrical rollerbearing, a tapered roller bearing, a spherical roller bearing, aneedle-shaped roller bearing, a thrust cylindrical roller bearing, athrust tapered roller bearing, a thrust needle-shaped roller bearing,and a thrust spherical roller bearing, and the like.

To form the coating film of the bismuth or the like on the surface ofthe bearing member made of metal, after the rolling bearing is immersedin a liquid in which the bismuth or the bismuth compound is dispersed,the bearing is rotated and by using frictional heat generated at thattime, the bismuth or the bismuth compound is allowed to react with thesurface of the metal. Thereby the coating film of the bismuth or thelike can be formed. An active metal surface is formed by friction or thelike on the surface of the bearing member made of metal. To form thecoating film quickly, it is desirable to form the coating film while theliquid is being warmed.

As other methods of forming the coating film of the bismuth or the like,dry plating such as vacuum evaporation, physical vapor deposition (PVD),chemical vapor deposition (CVD), and ion plating; and wet plating suchas electroplating, electroless plating, conversion treatment are listed.In addition, after at least one substance selected from among thebismuth and the bismuth compound is heated to a temperature higher thanthe melting point thereof, the substance or the substances are appliedto the surface of the bearing made of metal on which the coating film isto be formed. Thereby the coating film of the bismuth and the bismuthcompound can be also formed.

A roller bearing in which the grease of the present invention that isused therefor is enclosed is described below with reference to FIG. 1.FIG. 1 is a partly cut-out perspective view of the roller bearing. Inthe roller bearing, a roller 34 a is disposed between an inner ring 32and an outer ring 33 via a cage 35. The roller 34 a is subjected torolling friction between a rolling surface 32 a of the inner ring 32 anda rolling surface 33 a of the outer ring 33 and sliding friction betweenflange portions 32 b of the inner ring 32. To reduce the rollingfriction and the sliding friction, the grease for use in the rollerbearing is enclosed therein.

The bearing for the rolling stock includes a bearing for an axle and abearing for a main motor.

As the bearing for the axle, an RCT bearing is used. In the RCT bearing,because a flange of a bearing ring makes a sliding motion on a large endface of a roller and at a flange portion thereof, the lubricating oilfilm of the lubricating grease is liable to fracture. When thelubricating oil film has fractured, metal contact occurs to generate adisadvantage that heat generation and frictional wear increase.

As the bearing for the main motor, a cylindrical roller bearing and aball bearing are used. As described above, in the case of thecylindrical roller bearing, the lubricating oil film of the lubricatinggrease is liable to fracture on the large end face of the roller and atthe flange portion. In the ball bearing, sliding occurs between therolling element and the cage, and further differential sliding occursbetween the rolling element and the bearing ring. Thus the lubricatingoil film of the lubricating grease is liable to fracture.

The bearing of the present invention for use in the axle of the bearingfor use in the rolling stock is described below with reference to FIG.5. FIG. 5 is a sectional view of the bearing for the axle. Both endportions of an axle 55 are supported by a tapered roller bearing 51mounted on a frame (not shown) of the rolling stock. The tapered rollerbearing 51 includes an inner ring 52, an outer ring 53, a plurality oftapered rollers 54 which are interposed between the inner ring 52 andthe outer ring 53 and which rotatably roll, a inner ring spacer 56interposed between the adjacent inner rings 52, and an injection hole 57for supplying the grease to the tapered roller 59.

Regarding the bearing for use in the main motor, both end portions of arotary shaft of the motor at its output side are supported by thecylindrical roller bearing or the ball bearing mounted on the frame ofthe rolling stock. The cylindrical roller bearing or the ball bearingincludes an inner ring, an outer ring, a plurality of cylindricalrollers or balls which are interposed between the inner ring and theouter ring and rotatably roll, and an injection hole for supplying thegrease to the cylindrical rollers or the balls.

The rotational output of the main motor is transmitted from an outputrotary shaft thereof to a gear fitted on the output rotary shaftthereof. The rotation of the gear is transmitted to a gear fitted on anaxle as the rotation of the axle.

The roller bearing of the bearing for use in the rolling stock in whichthe rolling bearing of the present invention is used is described belowwith reference to FIG. 1. FIG. 1 is a partly cut-out perspective view ofthe roller bearing. In the roller bearing, the roller 34 a is disposedbetween the inner ring 32 and the outer ring 33 via the cage 35. Theroller 34 a is subjected to the rolling friction between the rollingsurface 32 a of the inner ring 32 and the rolling surface 33 a of theouter ring 33 and the sliding friction between the flange portions 32 bof the inner ring 32. To reduce the rolling and sliding frictions, thegrease for use in the roller bearing is enclosed therein.

A wheel-supporting apparatus in which the rolling bearing of the presentinvention is used is described below with reference to FIG. 6. FIG. 6 isa sectional view of the wheel-supporting apparatus. As shown in FIG. 6,a flange 63 and an axle 64 are provided on a steering knuckle 62, and anaxle hub 65 serving as a rotary member is rotatably supported by a pairof tapered roller bearings 61 a, 61 b mounted on an outside-diametersurface of the axle 64.

The axle hub 65 has a flange 66 on its outside-diameter surface. Abraking drum 69 of a braking apparatus and a wheel disk 70 of a wheelare mounted by a stud bolt 67 provided on the flange 66 and a nut 68engaging the stud bolt 67 with a screw. Reference numeral 71 denotes arim mounted on the outside-diameter surface of the wheel disk 70. A tireis mounted on the rim.

A back plate 72 of the braking apparatus is mounted on a flange 63 ofthe steering knuckle 62 by tightening a bolt and a nut. A brakingmechanism for imparting a braking force to the braking drum 69 issupported on the back plate 72. The braking mechanism is not drawn inFIG. 6.

A pair of the above-described tapered roller bearings 61 a, 61 brotatably supporting the axle hub 65 is lubricated by grease enclosedinside the axle hub 65. To prevent the grease from leaking from thetapered roller bearing 61 a and muddy water from penetrating into therolling bearing from the outside, a grease cap 73 is mounted on an outerend surface of the axle hub 65, with the grease cap 73 covering thetapered roller bearing 61 b.

One example of the tapered roller bearing of the present invention foruse in the wheel-supporting apparatus is described below with referenceto FIG. 2. FIG. 2 is a partly cut-out perspective view of the taperedroller bearing. In a tapered roller bearing 31 b, a tapered roller 34 bis disposed between the inner ring 32 and the outer ring 33 via the cage35. The tapered roller 34 b is subjected to rolling friction between therolling surface 32 a of the inner ring 32 and the rolling surface 33 aof the outer ring 33, and subjected to sliding friction between theflange portions 32 b and 32 c of the inner ring 32. To reduce therolling and sliding frictions, the grease for use in the roller bearingis enclosed therein.

A bearing for use in a rolling neck of a rolling machine in which therolling bearing of the present invention is used is described below withreference to FIG. 7. FIG. 7 is a sectional view of the bearing for usein the rolling neck of the rolling machine. As shown in FIG. 7, aclosed-type four-row tapered roller bearing 81 mounted on the rollingneck of the rolling machine has one inner ring 82 having rollingsurfaces 83 a, 83 b, 83 c, and 83 d disposed in four rows; a pair ofouter rings 84 a, 84 b having rolling surfaces 85 a, 85 d disposed in asingle row respectively; one outer ring 84 c having rolling surfaces 85b, 85 c disposed in two rows respectively; tapered rollers 86 rotatablydisposed in four rows between the rolling surfaces 83 a, 83 b, 83 c, and83 d of the inner ring 82 and the rolling surfaces 85 a, 85 d, 85 b, and85 c of the outer rings 84 a, 84 b, and 84 c; and a cage 87 holdingtapered rollers 86 circumferentially at predetermined intervals. A sealmember 88 is mounted at both end portions of each of the outer rings 84a, 84 b disposed at both sides of the bearing. A large flange 89 isprovided at a central portion of each inner ring 82. When the bearing isused, the tapered rollers 86 roll on the rolling surfaces 83, while thetapered rollers 86 are being guided by the large flange 89.

The tapered rollers 86 are subjected to rolling friction between therolling surfaces 83 a, 83 d of the inner ring 82 and the rollingsurfaces 85 a, 85 d, 85 b, and 85 c of the outer rings, and slidingfriction between flange portions 89 a, 89 b, 89 c, 89 d, 89 e, 89 f, 89g, and 89 h of the inner ring 82. To reduce the rolling and slidingfrictions, the grease for use in the roller bearing is enclosed therein.

The seal member 88 mounted on the end portion of each of the outer rings84 a, 84 b slidingly contacts the outside-diameter surface of the innerring 82, thus sealing the inside of the bearing. The seal member 88includes sealing cases 90 a, 90 b mounted at the end portion of each ofthe outer rings 84 a, 84 b disposed at both sides of the bearing and acontact-type oil seal 92 fitted in an annular groove 91 formed on theinside-diameter portion of each of the sealing cases 90 a, 90 b.

Four examples of the construction of the wheel-supporting rollingbearing unit preferable in carrying out the present invention aredescribed below.

A first example of the preferable construction of the wheel-supportingrolling bearing unit in which the rolling bearing of the presentinvention is used is shown in FIG. 8. The first example has aconstruction for supporting a driven wheel (front wheel of FR car and RRcar, rear wheel of FF car) and for reducing the rotational torque of thehub 7 b to a higher extent by improving the above-described constructionshown in FIG. 13. For this purpose, in the case of the first example, anopen portion of the inner end of an outer ring 20 is closed with a cap18 a, and the space between the inner peripheral surface of an outer endportion of the outer ring 20 and the peripheral surface of anintermediate portion of the hub body 23 is closed with a seal ring 16 c.Because the cap 18 a is provided, it is possible to omit the provisionof a seal ring 16 d, shown in FIG. 13, which is disposed between theinner peripheral surface of the inner end portion of the outer ring 20and the peripheral surface of the inner ring 24. The seal ring 16 c andthe cap 18 a prevent foreign matters such as muddy water frompenetrating into an inner space 17 b in which balls 14, 14 are mounted.0.01 to 15 wt % of the bismuth or the inorganic bismuth is added to theentirety of the grease to be enclosed in the inner space 17 b. Theconstructions of the other parts are similar to the conventionalconstructions shown in FIG. 13. When the wheel-supporting rollingbearing unit of the present invention is applied to the driven wheel,the seal ring is not provided between the inner peripheral surface ofthe inner end portion of the outer ring and the peripheral surface ofthe inner ring. Thus it is possible to make the rotational torque of thehub lower than that of the hub of the conventional wheel-supportingrolling bearing unit.

A second example of the preferable construction of the wheel-supportingrolling bearing unit of the present invention is shown in FIG. 9.

The second example has also a construction for supporting the drivenwheel (front wheel of FR car and RR car, rear wheel of FF car). In thecase of the second example, an external thread portion 27 is formed atan inner end portion of a hub body 23 a constituting a hub 7 c, and aninner end surface of an inner ring 24 fitted on a small-diameter steppedportion 25 of the hub body 23 a is held down with a nut 28 screwed onthe external thread portion 27. In conformity to this, a cap 18 bmounted on an open portion disposed at the inner end of an outer ring 20is bulged to prevent the external thread portion 27 and the nut 28 frominterfering with the cap 18 b. Other constructions are similar to thoseof the above-described first example.

A third example of the preferable construction of the wheel-supportingrolling bearing unit of the present invention is shown in FIG. 10. Thethird example has a construction for supporting a driving wheel (rearwheel of FR car and RR car, front wheel of FF car, all wheels of 4WDcar).

To realize this construction, in the case of the third example, a splinehole 29 is formed at a central portion of a hub body 23 b constituting ahub 7 d, serving as a rotational-side bearing ring, which is rotatablysupported on the inside-diameter side of the outer ring 20 serving as astationary-side bearing ring. In a state in which the bearing unit ismounted on a vehicle, a spline shaft (not shown) attached to theconstant velocity joint is inserted into the spline hole 29.

When the wheel-supporting rolling bearing unit of the present inventionis applied to the driving wheel, because the spline hole is formed atthe central portion of the hub body having the hub serving as therotational-side bearing ring, by connecting the spline shaft attached tothe constant velocity joint to the spline hole, the rotational torque ofthe constant velocity joint can be reliably transmitted to the hub.

The hub 7 d is constructed by holding down an inner end surface of aninner ring 24 fitted on a small-diameter stepped portion 25 formed at aninner end portion of the hub body 23 b by means of a caulking portion 26formed by plastically deforming the inner end portion of the hub body 23b radially outward and fixing the inner ring 24 to the hub body 23 b.Seal rings 16 c, 16 d are provided between inner peripheral surfaces ofboth end portions of the outer ring 20 and the peripheral surface of theintermediate portion of the hub body 23 b as well as the peripheralsurface of the inner end portion of the inner ring 24 to disconnect aninner space 17 b in which the balls 14, 14 are provided and an outerspace from each other between the inner peripheral surface of the outerring 20 and the peripheral surface of the hub 7 d. Other constructionsare similar to those of the above-described first and second examples.

A fourth example of the preferable construction of the wheel-supportingrolling bearing unit of the present invention is shown in FIG. 11. Thefourth example also has a construction for supporting the driving wheel(rear wheel of FR car and RR car, front wheel of FF car, all wheels of4WD car).

In the case of the fourth example, an inner end surface of an inner ring24, fitted on a small-diameter stepped portion 25 formed at an inner endportion of a hub body 23 c, which constructs a hub 7 e together with thehub body 23 c is projected inward from an inner end surface of the hubbody 23 c. In a state in which the bearing unit is mounted on a vehicle,an outer end surface of an unshown constant velocity joint strikesagainst the inner end surface of the inner ring 24. Thereby the innerring 24 is prevented from slipping off from the small-diameter steppedportion 25. Other constructions of the bearing unit of the fourthexample are similar to those of the bearing unit of the above-describedthird example.

The bismuth or the inorganic bismuth, the base oil, the thickener, andthe additive composing the grease that can be preferably applied to thefour examples of the above-described constructions of thewheel-supporting rolling bearing units of the present invention aredescribed below.

The wheel-supporting rolling bearing unit of the present invention inwhich the grease containing the bismuth or the inorganic bismuth can beenclosed is not limited to the above-described four examples of thewheel-supporting rolling bearing units of the present invention havingthe above-described constructions, but the grease containing the bismuthor the inorganic bismuth is applicable to the above-described twoexamples having the above-described conventional constructions.

The grease for use in the constant velocity joint is enclosed in theconstant velocity joint of the present invention. For example, as arepresentative constant velocity joint of a plunging type, a constantvelocity joint of a double off-set type and a constant velocity joint ofa tri-port type are known. As shown in FIG. 16, in the constant velocityjoint of the double off-set type, six track grooves 103, 109 are axiallyequiangularly formed on an inner surface of an outer ring 102 and anouter surface of a spherical inner ring 101, a ball 105 incorporatedbetween the track grooves 103 and 104 is supported by a cage 106, andthe periphery of the cage 106 is set as a spherical surface 107, and theinner periphery thereof is set as a spherical surface 108 fitting on theperiphery of the inner ring 101, and centers B, C of the sphericalsurfaces 107, 108 are axially shifted from each other on the axis of theouter ring 102.

The periphery of the outer ring 102 and the periphery of a shaft 109 arecovered with a boot 110, and a grease 111 of the present invention foruse in the constant velocity joint is filled and sealed inside the boot110. As described above, the plunging-type constant velocity joint hasmuch more sliding elements than rolling elements. The grease containingthe bismuth or the inorganic bismuth superior in the resistance to heatand durability is enclosed in the constant velocity joint of the presentinvention. Thus by supplying the bismuth or the inorganic bismuth torolling and sliding contact portions, the constant velocity joint iscapable of maintaining the extreme-pressure property effect for a longtime.

As shown in FIG. 17, in the constant velocity joint of the tri-porttype, three cylindrical track grooves 113 are axially equiangularlyformed on an inner surface of an outer ring 112, three leg-like shafts115 are provided on a tri-port member 114 incorporated at an inner sideof the outer ring 112, a spherical roller 116 is fitted on an outer sideof each leg-like shaft 115, a needle 117 is incorporated between thespherical roller 116 and the leg-like shafts 115 to thereby support thespherical roller 116 is rotatably and axially slidably, and thespherical roller 116 is fitted on the track groove 113.

The periphery of the outer ring 112 and the periphery of the shaft 109are covered with a boot 110, and the grease 111 for use in the constantvelocity joint of the present invention is filled and sealed inside theboot 110.

In the constant velocity joint of the plunging-type having theabove-described construction, owing engagement between the track grooves103, 109 and the ball 105 and between the track groove 113 and thespherical roller 116, the rotational torque is transmitted, and the ball105 and the spherical roller 116 roll along the track grooves 103 and113 respectively to absorb the torque.

When the rotational torque is transmitted in a state in which theconstant velocity joint takes an operational angle, in the constantvelocity joint of the double off-set type, rolling and sliding aregenerated in the fitting of the ball 105 on the track grooves 103, 104,and sliding is generated between the cage 106 and the outer ring 102 andbetween the cage 106 and the inner ring 101. On the other hand, in theconstant velocity joint of the tri-port type, rolling and sliding aregenerated between the track groove 113 and the spherical roller 116. Thegrease containing the bismuth or the inorganic bismuth superior in theresistance to heat and durability is enclosed in the constant velocityjoint of the present invention. Thus by supplying the bismuth or theinorganic bismuth to rolling and sliding contact portions, the constantvelocity joint is capable of maintaining the extreme-pressure propertyeffect for a long time.

The form of the rolling bearing of the present invention on which thecoating film of bismuth or the like is formed is not limited to aspecific form.

One example of the rolling bearing of the present invention is shown inFIG. 3. FIG. 3 is a sectional view of a deep groove ball bearing inwhich grease is enclosed.

In a deep groove ball bearing 31, an inner ring 32 having an inner ringrolling surface 32 a on its peripheral surface and an outer ring 33having an outer ring rolling surface 33 a on its inner peripheralsurface are concentrically disposed, and a plurality of rolling elements34 is disposed between the inner ring rolling surface 32 a and the outerring rolling surface 33 a.

The coating film of the bismuth or the like of the present invention isformed on at least one contact surface selected from among the surfacesof the inner ring rolling surface 32 a, the outer ring rolling surface33 a, and the rolling elements 34.

A cage 35 holding the rollers 34 and a seal member 36 fixed to the outerring 33 are provided at openings 38 a and 38 b, of the inner ring 32 andthe outer ring 33, disposed at both axial ends of the inner ring 32 andthe outer ring 33 respectively. It is essential to apply a grease 37 tothe peripheries of rollers 34.

The seal member 36 may be made of metal or rubber molding or may be acomposite of the rubber molding, a metal plate, a plastic plate, and aceramic plate. The composite of the rubber molding and the metal plateis preferable in consideration of durability and easiness in adherence.

Another example of the rolling bearing of the present invention is shownin FIG. 2. FIG. 2 is a partly cut-out perspective view of the taperedroller bearing. In the tapered roller bearing 31 b, the tapered roller31 b is disposed between the inner ring 32 and the outer ring 33 throughthe cage 35. The tapered roller 39 b is subjected to rolling frictionbetween the rolling surface 32 a of the inner ring 32 and the rollingsurface 33 a of the outer ring 33 and sliding friction between theflange portions 32 b and 32 c of the inner ring 32.

The coating film of the bismuth or the like of the present invention isformed on at least one contact surface selected from among the rollingsurface 32 a of the inner ring 32, the rolling surface 33 a of the outerring 33, and the surface of the tapered roller 34 b.

To reduce the rolling and sliding frictions, grease for use in therolling bearing is enclosed in the roller bearing.

As materials which can be used for the rolling parts of the presentinvention, known metal materials which can be adopted for bearing parts(inner and outer rings, rolling element, cage, and the like) are used,and the kind of the metal materials is not specifically limited. Asexamples of materials for use in the bearing ring, bearing steel(high-carbon chromium bearing steels JIS G 4805), steel for casehardening (JIS G 9104), high-speed steel (AMS6490), stainless steel (JISG 4303), and induction-hardened steel (JIS G 4051) are listed. Asmaterials for the cage, a steel plate (JIS G 3141) for a pressed cage,carbon steel (JIS G 4051) for a machined cage, and high-strength brasscasting (JIS H 5102) for the machined cage are listed. It is alsopossible to adopt white metal composed of gun metal, lead, and tin andother bearing alloys.

The coating film of the bismuth or the like should be formed on thecontact surfaces of the rolling parts that can be used in the presentinvention. The method of forming the coating film is not limited to aspecific method.

An apparatus for supporting a main shaft for wind power generation isdescribed with reference to FIGS. 18 and 19. FIG. 18 is an illustrationof an entire wind power generator including the apparatus for supportingthe main shaft for wind power generation. FIG. 19 shows the apparatusfor supporting the main shaft for wind power generation shown in FIG.18. As shown in FIGS. 18 and 19, in a wind power generator 121, a mainshaft 123 on which a blade 122 serving as a windmill is mounted isrotatably supported by a bearing 125 mounted in a bearing housing 135disposed inside a nacelle 124, and inside the nacelle 124, a speed-upgear 126 and a generator 127 are mounted. The speed-up gear 126increases the rotation of the main shaft 123 and transmits an increasedrotational speed thereof to an input shaft of the generator 127. Thenacelle 124 is pivotally mounted on a supporting base 128 through aswing bearing 140 and driven by a motor 129 of FIG. 19 for pivotal usethrough a reduction gear 130. The nacelle 124 is pivoted so that thedirection of the blade 122 confronts the direction of wind. Although twobearings 125 for supporting the main shaft are provided in the exampleof FIG. 19, the number of the bearings 125 may be one.

The mounted construction of the bearing 125 for supporting the mainshaft is described below with reference to FIG. 20. FIG. 20 shows themounted construction of the main shaft-supporting bearing 125 of theapparatus for supporting the main shaft for wind power generation. Thebearing 125 has an inner ring 131 and an outer ring 132 making a pair ofbearing rings and a plurality of rolling elements 133 interposed betweenthe inner ring 131 and the outer ring 132. The bearing 125 should be aradial bearing to which a thrust load is applicable and may be aspherical roller bearing and in addition an angular ball bearing, atapered roller bearing or a deep groove ball bearing. Of these bearings,the spherical roller bearing is preferable as a bearing for supportingthe main shaft for wind power generation which is driven in a region ofa wide range from a lightweight load to a heavy load applied at the timeof a sudden gust of wind and in a state in which the direction of windalways changes, because the spherical roller bearing is capable ofabsorbing the bending of the main shaft caused by the operation of theapparatus. The double row spherical roller bearing of the presentinvention in which the grease containing the inorganic bismuth isenclosed can be preferably used as a double row spherical roller bearingcapable of performing its function even though load capacities appliedto rows are different from one another and as the bearing for supportingthe main shaft for wind power generation in which a large thrust load isapplied as compared with a radial load and a larger load is applied to abearing portion of a row farther from a blade than a bearing portion ofa row nearer to the blade. This is because the double row sphericalroller bearing of the present invention is excellent in the frictionalwear and long-term durability thereof.

A raceway surface 132 a of the outer ring 132 of the bearing 125 isspherical, and the peripheral surface of each rolling element 133 isformed as a roller spherical along the raceway surface 132 a of theouter ring. The inner ring 131 has a flange-provided constructionseparately having raceway surfaces 131 a, 131 a of respective rows. Therolling elements 133 are held by cages 134 respectively for each row.

The outer ring 132 is mounted by fitting the outer ring 132 on theinside-diameter surface of the bearing housing 135, and the inner ring131 is fitted on the periphery of the main shaft 123 and supports themain shaft 123. In the bearing housing 135, a seal 136 such as alabyrinth seal is constructed between a side wall portion 135 a coveringboth ends of the bearing 125 and the main shaft 123. Because the bearinghousing 135 provides sealing property, a construction not having a sealis used for the bearing 125. The bearing 125 serves as the bearing forsupporting the main shaft for wind power generation according to anembodiment of the present invention.

EXAMPLES Examples 1 through 11

In a reaction container, as shown in table 1, a thickener was added tobase oil, and uniformalizing treatment was performed by using a tripleroll mill to obtain lithium soap/mineral oil-based grease (viscosity ofbase oil at 40° C.: 100 mm²/s, mixing consistency: 220), urea/PAOoil-based grease (viscosity of base oil at 40° C.: 46 mm²/s, mixingconsistency: 280), lithium soap/ester oil-based grease (viscosity ofbase oil at 40° C.: 33 mm²/s, mixing consistency: 250), and urea/etheroil-based grease (viscosity of base oil at 40° C.: 100 mm²/s, mixingconsistency: 300).

Further, as an extreme-pressure agent, bismuth or inorganic bismuth wasadded to the above-described grease at rates shown in table 1 to formgrease of each example. On the obtained grease, an extreme-pressureproperty evaluation test and a test of a roller bearing were conducted.Results are shown in table 1.

Comparison Example 1 through 8

In a reaction container, as shown in table 2, a thickener was added tobase oil, and uniformalizing treatment was performed by using a tripleroll mill to obtain lithium soap/mineral oil-based grease (viscosity ofbase oil at 40° C.: 100 mm²/s, mixing consistency: 220), urea/PAOoil-based grease (viscosity of base oil at 40° C.: 46 mm²/s, mixingconsistency: 280), lithium soap/ester oil-based grease (viscosity ofbase oil at 40° C.: 30 mm²/s, mixing consistency: 250), and urea/etheroil-based grease (viscosity of base oil at 40° C.: 100 mm²/s, mixingconsistency: 300).

Further as an extreme-pressure agent, organic bismuth, MoDTC or zincpowder was added to the above-described grease at rates shown in table 2to form grease of each comparison example.

Similarly to the examples 1 through 11, an extreme-pressure propertyevaluation test and a test of a roller bearing were conducted. Resultsare shown in table 2.

Extreme-Pressure Property Evaluation Test:

An extreme-pressure property evaluation test apparatus is shown in FIG.4. An evaluation test apparatus is constructed of a ring-shaped specimen42 of φ40×10 fixed to a rotary shaft 41 and a ring-shaped specimen 43whose end surface is rubbed with an end surface 44 of the specimen 42.The grease for the roller bearing was applied to the end surface 44, andthe rotary shaft 41 was rotated at 2000 rpm. An axial load of 490N inthe right-hand direction A in FIG. 4 and a radial load of 392 N wereapplied to evaluate the extreme-pressure property thereof. Theextreme-pressure property was evaluated by measuring vibrations of therotary shaft 41 generated owing to an increase of the frictional wear ofsliding portions of both specimens 42, 43 by a vibration sensor. Thetest was conducted until the vibration value of the rotary shaft 41became twice as large as an initial value thereof. The period of time ittook for the vibration value thereof to become twice as large as theinitial value thereof was measured.

The longer is the period of time it took for the vibration value thereofto become twice as large as the initial value thereof, the larger wasthe extreme-pressure property effect, and hence excellent resistance toheat and durability are shown. The resistance to heat and durability ofthe grease of each of the examples and the comparison examples wasevaluated by comparing the above-described measured time periods withone another.

Test of Roller Bearing:

3.6 g of grease was enclosed in each of 30206 tapered roller bearings,and the evaluation test apparatus was operated at an axial load of 980N, 2600 rpm, and a room temperature to measure the temperature of thesurface of the flange portion during the rotation thereof. An averagevalue of the temperature of the surface of the flange portion wascomputed in four to eight hours after the operation of the evaluationtest apparatus started.

As sliding friction generated between the flange portion and the“roller” becomes larger, the temperature of the surface of the flangeportion during the rotation thereof becomes increasingly high. Thereforethe resistance to heat and durability of the grease of each of theexamples and the comparison examples was evaluated by comparingabove-described measured temperatures with one another. That theabove-described measured temperature is not more than 70° C. was set asthe standard by which the grease is judged to have resistance to heatand durability.

TABLE 1 Example Grease 1 2 3 4 5 6 7 8 9 10 11 Base grease (wt %)Lithium soap/mineral-based grease 95 95 — — 99 85 — — 95 95 95 Urea/PAOoil-based grease — — 95 95 — — — — — — — Lithium soap/ester oil-basedgrease — — — — — — 95 — — — — Urea/ether oil-based grease — — — — — — —95 — — — Extreme-pressure agent (wt %) Bismuth sulfate  5 —  5 — — —  5— — — — Bismuth trioxide —  5 —  5  1 15 —  5 — — — Bismuth powder — — —— — — — — — —  5 Organic bismuth compound 1) — — — — — — — — — — —Bismuth carbonate — — — — — — — —  5 — — Sodium bismuthate — — — — — — —— —  5 — MoDTC 2) — — — — — — — — — — — Zinc powder — — — — — — — — — —— Extreme-pressure property evaluation test (h) 92 140  170  230  86190  76 88 53 54 300  Test of roller bearing (° C.) 66 64 58 56 68 67 5070 68 68 55

TABLE 2 Comparison example Grease 1 2 3 4 5 6 7 8 Base grease (wt %)Lithium soap/mineral-based grease 100 — — — 95 95 — 95 Urea/PAOoil-based grease — 100 — — — — 95 — Lithium soap/ester oil-based grease— — 100 — — — — — Urea/ether oil-based grease — — — 100 — — — —Extreme-pressure agent (wt %) Bismuth sulfate — — — — — — — — Bismuthtrioxide — — — — — — — — Bismuth powder — — — — — — — — Organic bismuthcompound₁₎ — — — —  5 —  5 — Bismuth carbonate — — — — — — — — Sodiumbismuthate — — — — — — — — MoDTC₂₎ — — — — —  5 — — Zinc powder — — — —— — —  5 Extreme-pressure property  16  39  6  14 54 16 62 20 evaluationtest (h) Test of roller bearing (° C.)  85  74  48  72 82 90 73 84₁₎Bismuth subgallate

₂₎Molyvan A (Vanderbilt Company Inc.) Molybdenum dithiocarbamate

Comparing data of the lithium soap/mineral oil-based grease of theexamples and the comparison examples shown in tables 1 and 2 with oneanother, in terms of the kind of the extreme-pressure agent, the bismuthor the inorganic bismuth was superior to the organic bismuth in theresistance to heat and the durability in the extreme-pressure propertyevaluation test and the test of the roller bearing.

As shown in the example 11 and the comparison example 5, the bismuthpowder has the resistance to heat and durability about six times aslarge as those of the organic bismuth. As shown in the example 2 and thecomparison example 5, the bismuth trioxide has the resistance to heatand durability about three times as large as those of the organicbismuth. From these results, it is considered that the bismuth or theinorganic bismuth is superior to the organic bismuth in the resistanceto heat and the durability, less heat-decomposable than the organicbismuth, and hence capable of keeping the extreme-pressure propertyeffect for a long time.

In the bismuth sulfate, the bismuth trioxide, and the bismuth powder,the bismuth powder showed the most favorable resistance to heat anddurability.

As the addition amount of the bismuth trioxide increases from 1 wt % ofthe example 5 to 5 wt % of the example 2 and to 15 wt % of the example6, there is a tendency that the extreme-pressure property effectincreases. But even though the addition amount of the bismuth trioxideincreases to 15 wt % three times as large as the addition amount of 5 wt%, the increase of the extreme-pressure property effect is about 1.4times. This is considered that when the addition amount of the bismuthtrioxide approaches 15 wt %, there is a tendency that the torque at thetime of the rotation is high and thus the generation of heat increasesand the rotation is interfered.

As shown in the comparison example 8, when the zinc powder is added tothe grease, the resistance to heat and durability of the greasedeteriorate considerably. Although the zinc powder is an inorganiccompound, no extreme-pressure property effect was admitted in the zincpowder. This is considered that because the melting point of zinc islow, the resistance of the grease to heat could not be improved.

Data of the urea/PAO oil-based grease, the lithium soap/ester oil-basedgrease, and the urea/ether oil-based grease of the examples and thecomparison examples shown in tables 1 and 2 were compared with oneanother. In the case of the urea/PAO oil-based grease, in terms of thekind of the extreme-pressure agents, the inorganic bismuth such as thebismuth sulfate and the bismuth trioxide was superior to the organicbismuth in the resistance to heat and durability thereof. As shown inthe examples 3, 4 and the comparison example 7, the bismuth trioxide hadresistance to heat and durability about three times as large as those ofthe organic bismuth, and the bismuth trioxide had resistance to heat anddurability about four times as large as those of the organic bismuth.This is considered that the inorganic bismuth is superior to the organicbismuth in the resistance to heat and durability thereof, lessheat-decomposable than the organic bismuth, and hence capable of keepingthe extreme-pressure property effect for a long time.

As shown in the example 7 and the comparison example 3, the lithiumsoap/ester oil-based grease containing the bismuth sulfate as theextreme-pressure agent had resistance to heat and durability about 13times as large as those of the ester oil-based grease not containing theextreme-pressure agent.

As shown in the example 8 and the comparison example 4, the urea/etheroil-based grease containing the bismuth trioxide as the extreme-pressureagent, the urea/ether oil-based grease had resistance to heat anddurability about six times as large as those of the urea/ether oil-basedgrease not containing the extreme-pressure agent. From these results, itis understood that the inorganic bismuth such as the bismuth sulfate andthe bismuth trioxide is capable of keeping the extreme-pressure propertyeffect for a long time.

Example 12

A copper plate (SUJ2, thickness: 10 mm) and a ring-shaped specimen(SUJ2) of φ40 mm×thickness of 10 mm were immersed in a solutioncontaining 5 g of the bismuth trioxide (produced by Wako Pure ChemicalIndustries, Ltd.) and 95 g of PAO oil (SYNFLUID 801 produced by NipponSteel Chemical Co., Ltd.) to which the bismuth trioxide was added. Thering-shaped specimen was rotated at 2000 rpm for 20 hours with an endsurface of the ring-shaped specimen pressed against the copper plate ata load of 490 N. By frictional heat generated at that time, a coatingfilm of the bismuth trioxide was formed on the end surface of thering-shaped specimen. The formation of the coating film of the bismuthtrioxide on the end surface of the ring-shaped specimen was confirmed bysurface analysis performed by means of Photoemission Spectroscopy(hereinafter referred to as XPS).

By using two ring-shaped specimens, an extreme-pressure propertyevaluation test shown below was conducted. Results are shown in FIG. 14.

Example 13

The copper plate (SUJ2, thickness: 10 mm) and the ring-shaped specimen(SUJ2) of φ40 mm×thickness:10 mm were immersed in a solution containing5 g of bismuth (produced by Wako Pure Chemical Industries, Ltd.) and 95g of the PAO oil (SYNFLUID 801 produced by Nippon Steel Chemical Co.,Ltd.) to which the bismuth was added. The ring-shaped specimen wasrotated at 2000 rpm for 20 hours with the end surface of the ring-shapedspecimen pressed against the copper plate at a load of 490 N. Byfrictional heat generated at that time, a coating film of the bismuthwas formed on the end surface of the ring-shaped specimen. The formationof the coating film of the bismuth on the end surface of the ring-shapedspecimen was confirmed by the surface analysis performed by means of theXPS.

By forming two ring-shaped specimens, an extreme-pressure propertyevaluation test shown below was conducted. Results are shown in FIG. 14.

Comparison Example 9

By using three ring-shaped specimens on which the coating film of thebismuth or the film of the bismuth compound was not formed, anextreme-pressure property evaluation test was conducted. Results areshown in FIG. 14. The materials and configurations of the ring-shapedspecimens were identical to those of the example 12.

Example 14

A 30204 tapered roller bearing was rotated in a solution containing 5 gof the bismuth trioxide (produced by Wako Pure Chemical Industries,Ltd.) and 95 g of the PAO oil (SYNFLUID 801 produced by Nippon SteelChemical Co., Ltd.) to which the bismuth trioxide was added. Each 30204tapered roller bearing was rotated at an axial load of 980 N and 2600rpm for eight hours to form the coating film of the bismuth trioxide onthe rolling surface of the 30204 tapered roller bearing. Two 30204tapered roller bearings were used and cleaned and a durability test ofthe rolling bearing shown below was conducted. Results are shown in FIG.15.

Example 15

The 30204 tapered roller bearing was rotated in a solution containing 5g of bismuth (produced by Wako Pure Chemical Industries, Ltd.) and 95 gof the PAO oil (SYNFLUID 801 produced by Nippon Steel Chemical Co.,Ltd.) to which the bismuth was added. The 30204 tapered roller bearingwas rotated at an axial load of 980 N and 2600 rpm for eight hours toform the coating film of the bismuth on the surface of the 30204 taperedroller bearing. Two 30204 tapered roller bearings were used and cleaned,and a durability test of the rolling bearing shown below was conducted.Results are shown in FIG. 15.

Comparison Example 10

By using two 30204 tapered roller bearings on which the coating film ofthe bismuth or the bismuth compound was not formed, a durability test ofthe rolling bearing was conducted. Results are shown in FIG. 15.

Durability Test of Rolling Bearing:

1.8 g of the lithium soap/mineral oil-based grease (ARAPEN RB300produced by Exxon Mobil Corporation) was enclosed in the 30204 taperedroller bearing. The tapered roller bearing was rotated at a temperatureof 120° C., and 5000 rpm, with an axial load of 67 N and a radial loadof 67 N applied thereto. The period of time (life period of time)required for the rotational torque of the bearing to increase not lessthan twice as large as an initial rotational torque thereof wasmeasured. The durability of the rolling bearing of each of the examples14, 15 and the comparison example 10 was evaluated by comparing theabove-described measured time periods with one another.

In FIG. 14 showing the extreme-pressure property evaluation test, thelife of the specimen of the comparison example 9 on which the coatingfilm of the bismuth or the like was not formed was 28 hours on theaverage, whereas the life of the specimen of the example 12 on which thecoating film of the bismuth trioxide was formed was 165 hours on theaverage which was 5.9 times as large as the life of the specimen of thecomparison example 9. Similarly as compared with the life of thespecimen of the comparison example 9, in the specimen of the example 13on which the coating film of the bismuth was formed, the vibrationvalues of the two specimens did not increase twice as large as theinitial vibration value even over 200 hours, and the extreme-pressureproperty evaluation test was terminated. Thus on the average, thespecimens of the example 13 showed an extreme-pressure property effectconsiderably exceeding 7.1 times that of the specimen of the comparisonexample 9.

These results indicate that by forming the coating film of the bismuthor the like, metal contact of the sliding portion is prevented and theextreme-pressure property effect was displayed. Further it is consideredthat of the coating films of the bismuth and the like, the coating filmof the bismuth is superior to that of the bismuth trioxide in thelong-term durability thereof. Thus the coating film of the bismuth has alarger extreme-pressure property effect than the bismuth trioxide.

In FIG. 15 showing the results of the durability test of the rollingbearing, the life of the specimen of the comparison example 10 on whichthe coating film of the bismuth or the bismuth compound was not formedwas 179 hours on the average, whereas the life of the specimen of theexample 14 on which the coating film of the bismuth trioxide was formedwas 395 hours on the average which was 3.9 times the life of thespecimen of the comparison example 10. Similarly as compared with thelife of the specimen of the comparison example 10, the specimen of theexample 15 on which the coating film of the bismuth was formed had alife of 500 hours on the average. Thus the specimen of the example 15showed durability 5.6 times as large as that of the comparison example10.

These results indicate that by forming the coating film of the bismuthor the like, metal contact at the flange portion of the roller bearingis prevented and the extreme-pressure property effect was displayed.Further it is considered that of the coating films of the bismuth andthe like, the coating film of the bismuth is superior to that of thebismuth trioxide in the long-term durability thereof, because thecoating film of the bismuth preventing the metal contact at the flangeportion of the roller bearing is stably present.

INDUSTRIAL APPLICABILITY

Because the inorganic bismuth excellent in the resistance to heat anddurability is used for the grease, rolling bearing, constant velocityjoint, and rolling parts of the present invention, the extreme-pressureproperty effect can be kept for a long time. Therefore the grease,rolling bearing, constant velocity joint, and rolling parts of thepresent invention can be preferably utilized for airplanes, rollingstocks, building machines, electric auxiliary machines of cars, hubs ofcars, and wind power generators and the like demanded to have resistanceto wear and long-term durability.

1-22. (canceled)
 23. A grease for use in a rolling bearing comprising abase grease and an additive, wherein the base grease comprises a baseoil and a thickener, said base oil is one oil selected from amongpoly-α-olefin oil, mineral oil, and ether oil, said base oil having akinematic viscosity of 33-100=²/s at 40° C. and the additive comprisesbismuth powder having a diameter of 5-500 μm.
 24. The grease accordingto claim 23, wherein 0.01 to 15 wt % of the bismuth powder is added to atotal amount of said base grease and said additive.
 25. The greaseaccording to claim 23, wherein said thickener is at least one compoundselected from among urea-based compounds and lithium soap.
 26. Thegrease according to claim 23 wherein said base oil is a poly-α-olefinoil.
 27. The grease according to claim 23 wherein said base oil is amineral oil.
 28. The grease according to claim 23 wherein said base oilis an ether oil.
 29. The grease according to claim 23, wherein saidbearing is for use in a rolling stock.